Mean rate of COPD exacerbations requiring oral or parenteral glucocorticosteroids (=moderate COPD exacerbations), or requiring hospitalization, or leading to death (=severe COPD exacerbations), per patient per year. A COPD exacerbation is an event in the natural course of the disease characterized by a change in the patient's baseline dyspnea, cough and/or sputum beyond day-to-day variability sufficient to warrant a change in management [American Thoracic Society (ATS) / European Respiratory Society (ERS) 2005].

The TDI is a recognized questionnaire to measure dyspnea in an out patient COPD population. At baseline, 3 components of dyspnea, each graded with 4 questions, were asked: - Functional Impairment - Magnitude of Task - Magnitude of Effort At each of the post-randomization visits questions from the TDI were asked related to 3 components: Change in - Functional Impairment - Magnitude of Task - Magnitude of Effort Each question in the TDI is graded from -3 (major deterioration) to +3 (major improvement). This results in a TDI Focal Score ranging from -9 to +9.

Shortness of Breath Questionnaire (SOBQ) Total Score [ Time Frame: Change from baseline over 24 weeks of treatment ]

Mean change from baseline during the treatment period in SOBQ. This is a 24-item measure that assesses self-reported shortness of breath while performing a variety of activities of daily living. The questions were administered at visits V0, V2, V3, V4, V5, V6 and Vend to assess the perceived shortness of breath of the patient. For each activity listed in the questionnaire the patient should rate his/her breathlessness on a scale between zero and five, where zero is "not at all breathless" and five is "maximally breathless or too breathless to do the activity".

The aim of the study is to compare the efficacy of roflumilast to placebo on pulmonary function and symptomatic parameters in patients with chronic obstructive pulmonary disease (COPD) during concomitant administration of tiotropium. The study duration will last up to 28 weeks. The study will provide further data on safety and tolerability of roflumilast.